Electrodeposition of zinc



' United States Patent 3,298,938 1 ELECTRODEPOSITION 0F ZINC YasuichiShibasaki, Yokohama, Japan, assignor to Kyowa Hakko Kogyo Co., Ltd.,Tokyo, Japan, a corporation of Japan N0 Drawing. Filed June 10, 1964,Ser. No. 374,178 Claims priority, application Japan, June 14, 1963,

' 38/ 30,527 5 Claims. (Cl. 20455) The present invention is concernedwith improvements in the electrodeposition of zinc. 'More specifically,it is concerned with improvements realized by the expedient of carryingout the electrodeposition of zinc in an aqueous electrolyte composition,sometimes referred to. as a bath, containing as principal ingredientammonia-alkaline zinc gluconate.

In the electrodeposition of zinc, e.g. in the electroplating orelectrowinning of this metal, use has generally been made, aselectrolytic bath, of an acidic zinc sulfate solution, of an alkalineZincate solution or of an alkaline zinc cyanide solution. The latterbath yields a smoother, more compact and more homogeneous deposit thanthe former. However, since the latter contains an extremely poisonouscyanide, the handling thereof is always accompanied by troublesomeproblems, e.g. disposal of cyanide-containing wastes.

It is a primary object of the present invention to embody anelectrolitic bath for zinc which contains no poisonous material, such asa cyanide or the like and which yields, at the least, essentially thesame result as an aqueous solution of alkali zinc cyanide inelectrodeposition. This and other objects can be realized by employingan aqueous solution of ammonia-alkaline zinc gluconate.

The concentration of Zinc gluconate in the baths useful according to thepresent invention for the electrodeposition of Zinc can vary over a widerange from dilute solution to saturated solution, but a concentrationranging from 0.1 to 2 molal (gram mols per kilogram of water) ispreferable and a concentration ranging from 0.5 -to 1.5 gram mols perkilogram of water.

The concentration of ammonia in the baths according to the presentinvention can also be varied in a wide range from dilute solution tosaturated solution; it is preferred, however, that the pH of the bath bein the range of from 7.5 to at 25 C.

A convenient method of preparing an electrolytic bath according to thisinvention is as follows:

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tinued when the pH reaches the desired value. The resulting solution isthen ready to function as an electrolytic bath according to thisinvention.

Alternatively, the bath can be prepared by dissolving zinc gluconate inwater, after which aqueous ammonia is added until the pH of theresulting ammoniacal solution attains the desired value. The so-preparedsolution is then also ready to function as an electrolyte bath accordingto the invention.

The electrolytic bath according to the invention can contain minoramounts of other additaments, such as ammonium gluconate, ammoniumcarbonate, surfactant, cobalt salt, dextrine, etc., Without impairingthe capability of the bath to result in good electrolytic precipitationof ZlIlC.

The mechanism of the electrodeposition is conventional. The electrolytecompositions according to the invention may be used to deposit zinc on avariety of:

objects to be Zinc-plated, e.g. steel plates, steel tools or machineparts may be plated. The object to be coated is made to constitute thecathode in usual manner, the anode being made of zinc and the directcurrent employed being introduced through the latter.

The plating solutions of the invention may be operated over a wide rangeof temperatures; best results being obtained at temperatures from about15 to 40 C. The current density may also vary considerably, as will beseen from the illustrative examples which follow. These examples setforth presently preferred embodiments for obtaining glossy zincdeposits.

Example 1 An aqueous ammonia-alkaline bath solution is preparedcontaining the following ingredients:

Zinc gluconate gram mols 1.5 Water kilograms 1 The pH of the solution isadjusted to 8 by the introduction of gaseous ammonia.

A steel stamping is connected up as cathode, and a zinc rod is used asanode. The electroplating operation is carried out at an electrolitesolution temperature of 16 C. Voltage of the electrolysis is 36 volts;current density of the electrodeposition (a./dm. is 25 amperes persquare decimeter.

At the end of 2 minutes, the electrodeposited Zinc coating is glossy,smooth and silver white.

Examples 2 to 4 These are carried out as described in Example 1, withZinc oxide, zinc hydroxide, zinc carbonate or the like the differencesshown in the following Table:

No. of Examples Example 2 Example 3 Example 4 Electrolyte solution:

Zinc gluconate 0.3 gram mol and 1.5 gram mol 1.5 gram mol and 0.5 gramof 0.1 gram mol of dextrin. hexaoxyethylene laurylether. Water 1 k 1 kg.PH controlled by the 8.5 8.

addition of ammonia. Temperature of electrolyte 15 C 40 0.

solution. Voltage of electrolysis. 10 v 2.7 v. 3.6 v. Current density ofelectro- 0.5 aJdm. 3 a. ldm. 4 aJdmA deposition. Time ofelectrodeposition 10 minutes 10 minutes 8 minutes. Textures of electro-Semi-glossy; Glossy; crystal- Glossy; slightly deposited zinc. slightlyrough; line; silver crystalline;

grey. white. silver white.

is added to an aqueous solution of gluconic acid of a desiredconcentration, thereby yielding an aqueous solution of zinc gluconate.After filtration, gaseous ammonia is passed into the solution (filtrate)while measuring the pH, introduction of ammonia being discon- Anelectrolytic bath according to the present invention presents thefollowing advantages:

(1) It makes possible electrodeposition of zinc of an excellence atleast equal to that obtained with an aqueous solution of, zinc cyanide,and sometimes of greater excellence.

(2) It yields a glossy zinc plating.

(3) It is bound up with ease of handling, since no special precautionshave to be taken such as are necessary when handling poisonous cyanide.

(4) Notwithstanding the simplicity of the bath composition, it resultsin excellent and stable electrolytic precipitation of zinc; moreover,disposition of the liquid is easy.

Having thus disclosed the invention, what is claimed is:

1. In a process for electrodepositing zinc wherein an electric currentis passed from a zinc anode to a cathode on which the zinc is to beelectrodeposited through an aqueous electrolyte solution, theimprovement wherein the said solution consists essentially of water,zinc gluconate, and sufli-cient ammonia to give a pH of 7.5 to 10.

2. Electrolytic bath for electrodepositing zinc consistin-g essentiallyof water, zinc gluconate, and suflicient ammonia to give a pH of 7.5 to10.

3. Electrolytic bath for electrodepositing zinc consisting essentiallyof water, zinc gluconate, and sufiicient ammonia to give a pH of 7.5 to'10, the concentration of zinc glucona-te "being in the range from 0.1to 2 gram mols per kilogram of water.

4. Electrolytic bath for electnodepositing zinc consist- 4 ingessentially of Water, zinc gluconate, and sufficient ammonia to give apH of 7.5 to 10, the concentration of zinc gluconate being in the rangefrom 0.5 to 1.5 gram mols per kilogram of water.

5. Aqueous electrolytic bath for electrodepositing zinc consistingessentially of water, zinc gluconate, and -am monia, the concentrationof the zinc gluconate being in the range from 0.5 to 1.5 :gram mols perkilogram of Water, and the pH of said bath being in the range from 7.5to 10, measured at 25 C.

References Cited by the Examiner UNITED STATES PATENTS 2,485,563.10/1949 Chester et a1. 204-- 2,537,032 1/1951 Chester et al. 204-552,576,997 12/1951' Chester 20455 2,576,999 12/1951 Chester et a1. 204-552,614,975 10 /1952 Chester 204-55 2,615,030 10/1952 Chester 204-55 X2,632,728 3/1953 Chester 204--55 2,799,635 7/1957 Chester et a1. 2-0455JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner.

1. IN A PROCESS FOR ELECTRODEPOSITING ZINC WHEREIN AN ELECTRIC CURRENTIS PASSED FROM A ZINC ANODE TO A CATHODE ON WHICH THE ZINC IS TO BEELECTRODEPOSITED THROUGH AN AQUEOUS ELECTROLYTE SOLUTION, THEIMPROVEMENT WHEREIN THE SAID SOLUTION CONSISTS ESSENTIALLY OF WATER,ZINC GLUCONATE, AND SUFFICIENT AMMONIA TO GIVE A PH OF 7.5 TO 10.